The present invention relates generally to providing network services such as load balancing, packet filtering or Network Address Translation (NAT). More specifically, network services are provided using a distributed architecture and packet fragments are handled using a fragment service manager.
As the IP protocol has continued to be in widespread use, a plethora of network service appliances have evolved for the purpose of providing certain network services not included in the protocol and therefore not provided by standard IP routers. Such services include NAT, statistics gathering, load balancing, proxying, intrusion detection, and numerous other security services. In general, such service appliances must be inserted in a network at a physical location where the appliance will intercept all flows of interest for the purpose of making its service available.
FIG. 1 is a block diagram illustrating a prior art system for providing a network service. A group of clients 101, 102, and 103 are connected by a network 110 to a group of servers 121, 122, 123, and 124. A network service appliance 130 is physically located in the path between the clients and the servers. Network service appliance 130 provides a service by filtering packets, sending packets to specific destinations, or, in some cases, modifying the contents of packets. An example of such modification would be modifying the packet header by changing the source or destination IP address and the source or destination port number.
Network service appliance 130 provides a network service such as load balancing, caching, or security services. In providing security services, network service appliance 130 may function as a proxy, a firewall, or an intrusion detection device. For purposes of this specification, a network service appliance that acts as a load balancer will be described in detail. It should be noted that the architecture and methods described are equally applicable to a network service appliance that is functioning as one of the other above described devices.
Network service appliance 130 is physically located between the group of servers and the clients that they serve. There are several disadvantages to this arrangement. First, it is difficult to add additional network service appliances when the first network service appliance becomes overloaded because the physical connections of the network must be rerouted. Likewise, it is difficult to replace the network service appliance with a back up network service appliance when it fails. Since all packets pass through the network service appliance on the way to the servers, the failure of the network service appliance may prevent any packets from reaching the servers and any packets from being sent by the servers. Such a single point of failure is undesirable. Furthermore, as networks and internetworks have become increasingly complex, multiple services may be required for a single network and inserting a large number of network service appliances into a network in places where they can intercept all relevant packet flows may be impractical.
The servers may also be referred to as hosts and the group of servers may also be referred to as a cluster of hosts. If the group of servers has a common IP address, that IP address may be referred to as a virtual IP address (VIPA) or a cluster address. Also, it should be noted that the terms client and server are used herein in a general sense to refer to devices that generally request information or services (clients) and devices that generally provide services or information (servers). In each example given it should be noted that the roles of client and server may be reversed if desired for a particular application.
A system that addresses the scalability issues that are faced by network service appliances (load balancers, firewalls, etc.) is needed. It would be usefult to distribute functions that are traditionally performed by a single network element and so that as much function as possible can be performed by multiple network elements. A method of coordinating work between the distributed functions with a minimum of overhead is needed.
Although network service appliances have facilitated the development of scalable server architectures, the problem of scaling network service appliances themselves and distributing their functionality across multiple platforms has been largely ignored. Network service appliances traditionally have been implemented on a single platform that must be physically located at a specific point in the network for its service to be provided.
For example, clustering of servers has been practiced in this manner. Clustering has achieved scalability for servers. Traditional multiprocessor systems have relatively low scalability limits due to contention for shared memory and I/O. Clustered machines, on the other hand, can scale farther in that the workload for any particular user is bound to a particular machine and far less sharing is needed. Clustering has also facilitated non-disruptive growth. When workloads grow beyond the capacity of a single machine, the traditional approach is to replace it with a larger machine or, if possible, add additional processors within the machine. In either case, this requires downtime for the entire machine. With clustering, machines can be added to the cluster without disrupting work that is executing on the other machines. When the new machine comes online, new work can start to migrate to that machine, thus reducing the load on the pre-existing machines.
Clustering has also provided load balancing among servers. Spreading users across multiple independent systems can result in wasted capacity on some systems while others are overloaded. By employing load balancing within a cluster of systems the users are spread to available systems based on the load on each system. Clustering also has been used to enable systems to be continuously available. Individual application instances or machines can fail (or be taken down for maintenance) without shutting down service to end-users. Users on the failed system reconnect and should not be aware that they are using an alternate image. Users on the other systems are completely unaffected except for the additional load caused by services provided to some portion of the users that were formerly on the failed system.
In order to take full advantage of these features, the network access must likewise be scalable and highly available. Network service appliances (load-balancing appliances being one such example) must be able to function without introducing their own scaling limitations that would restrict the throughput of the cluster. A new method of providing network services using a distributed architecture is needed to achieve this.
In a distributed architecture for providing network services, all fragments of a flow may not pass through the same node that is providing a network service. For example, if a router is being used to distribute packets among a group of servers, then some IP packets might be fragmented and some of the fragments might pass through the router with other fragments passing through other routers. In addition, a complete flow identifier may not be derivable from each of the fragments. Therefore a method of handling fragments in a distributed architecture for providing network services is needed.
A system that includes a fragment service manager that collects packet fragments from forwarding agents is disclosed. The fragment service manager sends directions to forwarding agents that specify packets fragments that the fragment service manager is prepared to assemble. The forwarding agents then forward such packet fragments to the fragment service manager. The fragment service manager assembles the packet fragments into complete packets and then determines a service manager that is to receive the complete packets. The fragment manager then forwards the complete packet to the service manager that is to receive the packet. Thus, the forwarding agents forward packet fragments to the fragment service manager and the fragment service manager assembles the packet fragments into complete packets and forwards the packets to the appropriate service manager. Packet fragments with insufficient information to determine a flow identifier that may be checked for a wildcard or fixed affinity match are assembled into a packet for which flow information may be obtained.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. Several inventive embodiments of the present invention are described below.
In one embodiment, a method of providing a network service includes sending a fragment criteria from a service manager to a forwarding agent that instructs the forwarding agent how to determine whether a received packet fragment at the forwarding agent matches the fragment criteria. A matching packet fragment is received from the forwarding agent at the fragment service manager. The fragment is assembled into a packet at the fragment service manager and in the event that the fragment completes the packet, a flow identifier specifying a flow is determined from the completed packet and completed packet is sent to a service manager that handles the flow specified in the flow identifier.
In another embodiment, a method of providing a network service includes implementing a forwarding agent on a network device. The forwarding agent stores one or more fragment criteria received from a fragment service manager. A packet fragment is received at the forwarding agent. It is determined whether the fragment matches the fragment criteria. The fragment is forwarded from the forwarding agent to the fragment service manager in the event that the fragment matches the fragment criteria so that the fragment may be assembled into a packet at the fragment service manager. In the event that the fragment completes the packet, a flow identifier specifying a flow may be determined from the completed packet and the completed packet may be sent to a service manager that handles the flow specified in the flow identifier.
In another embodiment, a forwarding agent includes a fragment service manager receiving interface for receiving instructions from a fragment service manager specifying fragment criteria for packet fragments that are to be sent to the fragment service manager. A fragment service manager sending interface sends packet fragments to the fragment service manager. A network packet receives interface for receiving IP packet fragments from a network. A processor determines whether packet fragments received on the network packet receiving interface match the fragment criteria.
In another embodiment, a fragment service manager includes a fragment criteria sending interface configured to send fragment criteria to a plurality of forwarding agents. The fragment criteria specify fragments that are to be sent to the fragment service manager. A fragment receiving interface is configured to received fragments matching the fragment criteria from the plurality of forwarding agents. A fragment processor is configured to assemble the received fragments into packets. A packet processor configured to determine a designated service manager for handling the assembled packets.